As a current collector for a negative electrode or an electrode of a battery cell, particularly a secondary cell, a rolled copper foil and an electrolytic copper foil have been used. Any of the copper foils is demanded to have high adhesiveness between a positive electrode or negative electrode active substance and the copper foil as a current collector. For improving the adhesiveness, there are cases where a surface treatment for forming unevenness on the surface of the copper foil is performed. For example, as described in PTL 1, the surface of the copper foil is abraded with emery paper to form unevenness, which targets the improvement in adhesiveness.